The present invention relates to a digital paging system, and more particularly to a digital paging system permitting both transmission and reception of a paging code including an address code and a message code.
In digital paging systems there are both higher and lower limits to the rate of transmission because of the need for efficient use of frequencies and because of the fear of a decrease in the probability of receiving the paging code due to an increase in the bit error rate (BER). Meanwhile, there are many proposals for paging systems in which message codes expressed in numerals or letters are transmitted as well as address or caling codes. In the proposed systems the paging receivers receive and display such message codes. One of the known examples of such proposals is the "Digital Radio Paging Communication System," disclosed by M. Masaki in the U.K. Patent Application Disclosure No. 2,061,582, which was assigned to the present application and made public on May 13, 1981. The transmission of message codes by such a system requires a transmission capacity twice or three times as great as that for mere address codes because each message code usually contains a large quantity of information. Therefore, the length of time during which the communication line is occupied by each subscriber tends to be extended, and inevitably the subscriber capacity of the whole system is correspondingly limited. This shortcoming could be overcome by raising the transmission rate, but it would again entail, as stated above, a decrease in paging code reception probability. Particularly, the decrease of the address code reception probability is fatal to the paging system because the paging receiver starts processing the message codes following its address code only after the latter has been correctly detected.